Evolution: Change in the genetic

composition of a population over

generational time

• Focus on adaptation through natural selection (not use/disuse)
  • characteristics that enhance fitness
  • these characteristics are heritable

?Could new species arise from an ancestral form by adaptions to different environments?

(1) Individuals in a population vary in their traits

?What is a trait?

Trait variation comes from random mutations

(2) Some of these differences are heritable

(3) In each generation, many more offspring are produced than can survive

• Only some will survive to reproduce
  
• Some will produce more offspring than others

(4) Individuals with certain heritable traits are more likely to survive and reproduce (adaptation)

• Individuals with certain traits produce more offspring than those without those traits (selection)
  
• Individuals are selected naturally, by the environment
  
• Favorable traits accumulate in a population

• Droughts cause shifts in beaks of finches on the Galapagos Islands
  • selection pressures from a single food source

• Average beak depth increases over time because deep-beaked individuals had greater reproductive success
  • the individuals during drought do not adapt beak size!

• Penicillin used in 1943 to stop S.aureus
  • by 1945 20% of S.aureus resistant
  • due to new enzyme ’penicilinase"

• Methicillin used in 1959 to stop S.aureus
  • deactivates production of cell walls
  • resistant strains emerged within 2 years
  • evolved a different enzyme to make cell walls

• Natural selection then lead to spread of MRSA
  • Methicillin-resistant S.aureus super bugs!
  • MRSA now resistant to multiple antibiotics

• Antibiotic resistance is ancient and widespread
  • genes to protect against penicillin, tetracycline, etc.
  • soil bacteria are rich in resistance

• Multi-drug resistance common in bacteria isolated from Lechuguilla Cave
  • ecosystem isolated from surface for 4 million years
  • Paenibacillus cave isolate is resistant to most clinical antibiotics
  • 18 resistance mechanisms, including 3 unknown!

If you were a bacteria today, in 2020….

Humans = ~25 years
Bacteria = ~20 minutes

How long is the average course of antibiotic treatment?